subagent handling + 1m context resume

dev/fake_upstream.py

@@ -7,7 +7,8 @@ lets us make Claude Code render its client-side tool UIs (AskUserQuestion,
 ExitPlanMode, TodoWrite/Task*) on demand, so the pane's frame detector in
 `src/term.rs` can be developed against what Ink actually draws.
 
-Scenario is picked per turn from `CT_FAKE_SCENARIO` (ask | plan | todo | text).
+Scenario is picked per turn from `CT_FAKE_SCENARIO`
+(ask | plan | todo | taskupdate | agent | text).
 Each incoming request is logged to `dev/fake_upstream.log` (declared tool names
 + the trailing user text) so we can see what CC sends.
 """
@@ -136,6 +137,19 @@ TASK_INPUTS = [
 ]
 
 
+# Two parallel subagents with the *same* type and byte-identical prompts: the
+# worst case for correlation (only Claude Code's `x-claude-code-agent-id` tells
+# them apart), and what makes the subagent rows worth having.
+AGENT_INPUTS = [
+    {"subagent_type": "Explore", "description": "find the retry helper",
+     "prompt": "Locate the retry helper and report back.", "run_in_background": False},
+    {"subagent_type": "Explore", "description": "find the retry helper",
+     "prompt": "Locate the retry helper and report back.", "run_in_background": False},
+    {"subagent_type": "oracle", "description": "review the lane design",
+     "prompt": "Review the lane design and report back.", "run_in_background": True},
+]
+
+
 class Handler(BaseHTTPRequestHandler):
     protocol_version = "HTTP/1.1"
 
@@ -161,7 +175,12 @@ class Handler(BaseHTTPRequestHandler):
         has_result = bool(blocks) and all(
             b.get("type") == "tool_result" for b in blocks if isinstance(b, dict)
         ) and "toolu_fake" in json.dumps(blocks)
-        log(f"[{time.strftime('%H:%M:%S')}] {self.path} tools={tools} tail={tail}")
+        # `model` + `anthropic-beta` show how a `--model opus[1m]` pick reaches
+        # the wire (the 1M context window is a beta header, not a model id).
+        log(
+            f"[{time.strftime('%H:%M:%S')}] {self.path} model={body.get('model')} "
+            f"betas={self.headers.get('anthropic-beta', '')} tools={tools} tail={tail}"
+        )
 
         if "count_tokens" in self.path:
             out = json.dumps({"input_tokens": 100}).encode()
@@ -190,6 +209,12 @@ class Handler(BaseHTTPRequestHandler):
                 gen = stream_tools(
                     [("TaskCreate", t) for t in TASK_INPUTS], "Setting up the task list."
                 )
+        elif scenario == "agent":
+            # Spawn subagents. A real child then issues their requests itself,
+            # each carrying `x-claude-code-agent-id`.
+            gen = stream_tools(
+                [("Agent", a) for a in AGENT_INPUTS], "Delegating this."
+            )
         elif scenario == "taskupdate":
             gen = stream_tool("TaskUpdate", {"taskId": "1", "status": "in_progress"},
                               "Starting the first task.")